That slimy pinkish-orange scum you see in your bathroom tub is the result of insufficient tub cleaning. It occurs due to either hard water or a strain of bacteria -- the latter of which can cause adverse health effects. Hard water will not cause any health issues other than possible damage to your hair. Regular tub cleaning as well as proper ventilation will help keep both possibilities for orange tub build-up from coming back and contribute to better health and deterioration of bathroom fixtures.
One of the possible causes for orange build-up in your tub or shower is from hard water. Hard water means your water carries an excess of minerals, including calcium, limestone and magnesium. The orange slime occurs through a combination of moisture, iron content and soap scum as the rusty iron colour attaches itself to soap scum around drains and faucets. Though bathing in hard water does not have any health risks it can tarnish your tub, sinks and other fixtures over time.
The other potential cause for orange build-up in your tub is serratia marcescens, a bacteria that is actually more reddish-pinkish in colour. This bacteria is found in dust, human and animal waste, surface water or any damp location. It commonly occurs in pets' water dishes, shower stalls and tubs. If the bacteria finds its way into the human system numerous health problems may result including meningitis, eye infections, urinary and respiratory tract infections and wound infections.
Hard Water Treatment
Remove hard water stains by wiping them with rubbing alcohol or with a lemon juice and water solution. Squeeze half a lemon into a 591ml. spray bottle and spray affected areas in your tub. Let stand for about 10 minutes, then wipe the mixture off. Repeat as needed to completely remove stains. Another option is to soak a scrubby rag in white vinegar to clean stains. Household chemical treatments are also options -- but research proper dilution techniques before applying chemicals to fixtures. Options include ammonia, oxalic acid and hydrochloric acid.
Remove serratia marcescens by spraying it with a mixture of 1/4 cup of white vinegar for every cup of water used. Spray liberally on affected areas and scrub off with an old toothbrush or scrub brush. Other options include scrubbing with a 50/50 solution of chlorine bleach and water, and reducing the humidity in the bathroom by leaving the door open and turning on the bathroom fan. Keeping the lights on is another option in terms of reducing humidity. Scrub your tub regularly to keep the mould from coming back.